Electrical systems in residential, commercial and industrial applications usually include a panelboard for receiving electrical power from a utility source and distributing electrical power to one or more branch circuits. The power is generally routed through overcurrent protection devices to designated branch circuits supplying one or more loads. The overcurrent protection devices are typically circuit interrupters such as circuit breakers and fuses which are designed to interrupt the electrical current supplied to the loads if certain predefined limits of the conductors are surpassed.
Circuit breakers are a well-known type of circuit interrupter which are often selected because a resetting mechanism allows their reuse. Typically, circuit breakers interrupt an electric circuit due to a disconnect or trip condition such as a current overload or ground fault. The current overload condition results when a current exceeds the continuous rating of the breaker for a time interval determined by the trip curve. The ground fault trip condition is created by an imbalance of currents flowing between a line conductor and a neutral conductor such as by a grounded conductor, or other current path to ground, or sometimes, by an arcing fault to ground.
However, arcing faults are often undetected by standard circuit breakers. An arcing fault is defined as current through ionized gas between two ends of a broken conductor, between two conductors supplying a load, or between a conductor and ground. Upon occurrence of an arcing fault, branch or load impedance may cause the current levels to be reduced to a level below the trip curve settings of the circuit breaker, causing the arcing fault condition to be undetected by the circuit breaker. In addition, an arcing fault which does not contact a grounded conductor or other grounded point will not trip a ground fault protected circuit.
There are many conditions that may cause an arcing fault, for example, corroded, worn or aged wiring or insulation, loose connections, wiring damaged by nails or staples through the insulation, and electrical stress caused by repeated overloading, lightning strikes, etc. These faults may damage the conductor insulation and/or create an unacceptably high temperature in the conductor.
Arcing fault detection systems/arcing fault circuit interrupters (AFCI) known in the art generally sense the current passing through the line conductor of a branch circuit, process the sensed information to determine whether the characteristics of the line current represent the occurrence of an arcing fault, and trip open the branch circuit if an arcing fault has occurred. Several arcing fault detection systems of this type are described in U.S. Pat. No. 5,682,101, in pending U.S. patent application Ser. No. 09/026,193 entitled "Electrical Fault Detection System" (Attorney's Docket NBD-27/SQRE020), and in pending U.S. patent application Ser. No. 09/129,685 (Attorney's Docket NBD-27-1/SQRE171) entitled "Arc Fault Detection System," all of which are assigned to the assignee of the present invention and are incorporated herein by reference. The arcing fault detection system may sense electrical properties other than line current.
There is a need for a simple and effective method and system to facilitate testing of an arcing fault circuit interrupter in a branch circuit. The present invention is directed to providing such a method and system. It is capable of producing simulated arcing faults in the branch circuit and determining whether the arcing fault detector trips i.e., interrupts the circuit in response to the simulated arcing condition. In one embodiment, the apparatus of the invention is capable of being enclosed within a relatively small, portable housing to facilitate independent testing of multiple branch circuits.